1. Field of the Invention
The present invention relates to a compactor machine for compressively forming granular materials into a desired shape, and more particularly to a compactor machine including at least one pair of compaction rolls.
2. Description of the Prior Art
It is a well known method to form granular materials into pieces of compacted material or so-called briquets by compacting the same by a pair of compaction rolls into elongate intermediate strips and then cutting the latter in a succeeding process.
This method is broadly utilized for preparing and/or processing granular or particulate materials for use in various industrial fields, e.g. chemical, food, pottery, mine, iron and steel making, particularly in making pellets for a blast furnace, and the like.
One known apparatus for performing such method is, for instance, a compactor machine. A first type of compactor machine includes a pair of cooperative forming or compaction rolls, in which a mass of granular material is fed continuously into forming paths defined between two rolls to thereby form a number of elongate intermediate strips, and then the strips are transversely cut into pieces of compacted material, i.e. briquets. There is a second type of prior compactor machine which includes a pair of compaction rolls having a plurality of forming recesses or pockets on peripheries thereof. The two rolls rotate cooperatively to jointly compact granular materials therebetween and thus directly form a plurality of briquets.
U.S. Pat. No. 4,033,559 discloses a compactor machine of the first type in which an intermediate flat strip having been formed between the pair of compaction rolls is horizontally or transversely split into strips by a slitter unit and then thus split strips are vertically cut into small pieces by a breaker unit. Provision of the slitter and breaker units is effective in exerting a stable cutting operation. However, it is disadvantageous in view of a compact or simple construction, since the two units are provided separately from the machine.
In view of the cutting means of the intermediate compacted material, a rotary hammer as disclosed, for instance, in Japanese Patent Laid-Open Publication No. 59-153599, and a rotary shear blade as disclosed, for instance, in U.S. Pat. No. 4,076,520 have been proposed. The rotary hammer strikes the intermediate strips to separate abruptly the latter into briquets with an impact force created by striking motion thereof. Thus separated briquets tend to have a decreased firmness due to a mechanical stress caused by such an abrupt impact force. Therefore only briquets of an increased brittleness are produced. These briquets have rough surfaces and thus a low surface density. Such surface become disadvantageous especially when reduced metal such as sponge iron is formed into briquets for the purpose of prevention of re-oxidization thereof.
The rotary shear blade also cuts the intermediate material into briquets with its shearing force, which also results in a similarly rough surface of the briquets.
With regard to compaction rolls, the first typed compactor machine generally includes a pair of rolls having a plurality of annular peripheral grooves and projections both extending in parallel and alternately in an axial direction. The grooves and projections of one roll are dislocated axially with respect to the grooves and projections of the other roll, respectively, such that the grooves of one roll and the projection of the other roll are disposed in registry with one another, and hence the projections of one roll and the grooves of the other roll are disposed in registry with one another. Thus the mating pair of groove and projection of the other roll jointly define a forming path therebetween at a position where the two rolls are confront each other.
When a mass of ganular material is compacted through the forming paths, the thus compacted material is highly detachable from walls of the groove and of the projection because of differences in peripheral rotational speed of the groove wall and the projection wall. As a result, the compaction rolls thus constructed may fail to exert compaction forces on the material since the material passes through the forming paths due to an insufficient retaining force acting on the same when the material has a relatively low viscosity. On the contrary, when a material of high viscosity is fed or an otherwise insufficient amount of the material is fed, a portion of the material moves along together with the walls of the grooves and/or the projections without being detached from the latter. The foregoing failures of the passing-through and the attaching impair a smooth operation of the machine and stable forming of the briquets.
In addition to those compaction rolls and the shearing means, a material feeder means is also important in achieving stable compaction forming. The prior compactor machine includes a feeder mechanism for guiding granular material therealong to feed the same into forming paths defined by and between the compaction rolls in which the material is preliminarily compressed to force out an air contained therein for thereby increasing a bulk density of the material.
One known feeder mechanism as shown in FIGS. 38 and 39 of the accompanying drawings includes a reversed frustoconical hopper 100 and a throat member 101 having a lower open end opening to an inlet space Z between the two rolls 200, and a tapered screw 103 for forcibly conveying the material toward the lower end . The lower open end of the throat member in the form of a circle, in which a lower end portion of the screw 103 is disposed and the lower end portion having a diameter A. The precompacted material M is fed into the inlet space Z defined between confronting peripheral portions of the rolls 200 extending between a first plane extending through axes of the rolls to pass a nip point N of the latter and a second planes extending respective axes of the rolls to a circular edges of the lowermost end portion of the tapered screw 103, and by a horizontal plane extending on the lower open end of the throat member 101. The second planes are slanted at an angle or nip angle .beta. with respect to the first plane about the respective axes of the rolls. A pair of triangular cheek plates 102 are provided at the lower end so as to seal opposite lateral openings of the inlet space in a pair of vertical parallel planes extending on opposite end surfaces of the rolls. As better shown in FIG. 36, the horizontal cross section of the hopper is a circle A, while the horizontal cross section of the inlet space is a rectangular shape. Consequently, when a mass of the material having been precompacted by cooperation of the tapered screw and the downwardly tapered screw and the downwardly tapered hopper is conveyed through a relatively narrow hopper throat of the circular cross section into a larger inlet space including a space X of the rectangular cross section, volumetric restriction given by the narrow throat is suddenly relieved, with the result that the precompacted material tends to bulge and thus recover its initial bulk density. More specifically, the material firstly confined within a space having the cross section of the circle A is released into the larger space having an increased volume X illustrated by hatched lines in FIG. 36.
Another prior compactor machine has a pair of compaction rolls having a relatively larger width W2 as schematically illustrated in FIG. 35, in which a pair of tapered screws are disposed in an adjacent parallel relation. Such tapered screws have lower end portions of a diameter O being about half the width W2. The two rolls are spaced apart from each other by a gap G at the nip point N.